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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Continuous Requirements Engineering in Sociotechnical Systems: Challenges and Solutions</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Marite Kirikova</string-name>
          <email>marite.kirikova@rtu.lv</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>A. Specifics of Sociotechnical Systems</institution>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Department of Artifical Intelligence and Systems Engineering, Riga Technical University Riga</institution>
          ,
          <country country="LV">Latvia</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>-Continuous requirements engineering in sociotechnical systems faces the challenges that originate from diverse and fast changes in systems contexts, project-based issues, and the multi-systems nature of sociotechnical systems. The interplay of these challenges and reported suggested treatments point to the necessity for flexible frameworks and new ways of knowledge management in systems development projects that concern sociotechnical systems.</p>
      </abstract>
      <kwd-group>
        <kwd>sociotechnical systems</kwd>
        <kwd>requirements engineering</kwd>
        <kwd>continuous engineering</kwd>
        <kwd>knowledge management</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>-</title>
      <p>Section II ponders over the necessity of continuity in
requirements engineering in sociotechnical systems. Section
III discusses challenges and treatments in agile projects.
Section IV concerns the challenges that stem from the
multisystems nature of sociotechnical systems. Section V suggests
some solutions for meeting the challenges discussed in
sections III and IV. Section VI concludes the paper with the
emphasis on the need for new forms of knowledge
management in continuous requirements engineering in
sociotechnical systems.</p>
      <p>
        II. WHY CONTINUITY IN REQUIREMENTS ENGINEERING
“A sociotechnical system is one that considers requirements
spanning hardware, software, personal, and community
aspects”. [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ] Therefore in sociotechnical contexts it is
necessary to be concerned about the different subjects and
objects of requirements at different levels of abstraction and
decomposition. The diversity of objects and subjects is
accompanied by their different speeds of action, life cycles,
and mutual relationships. All of the aforementioned aspects
are sources of possible changes in requirements that can
happen in both predictable and unpredictable situations and
time points. To embrace this diverse and fast changing
environment of requirements, the continuous handling of such
requirements, based on a good understanding of systems
involved, can be derived as a logical means for requirements
engineering. Some of the reasons for continuity in
requirements engineering of sociotechnical systems are shown
inf Fig. 1.
      </p>
      <p>Fig.1. Reasons for continuity in requirements engineering.</p>
      <p>
        The reasons are structured in three groups. The first group
of reasons derives from the nature of projects that are
performed for developing the constituents of sociotechnical
systems [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. Agile approaches work with the artifacts (e.g.,
user stories) that differ from the ones used in traditional
requirements engineering. As a result, several challenges are
reported by researchers and practitioners [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
      </p>
      <p>Another group of challenges stems from the variable
nature of systems to be considered in sociotechnical contexts.
It is not only that social and technical aspects are to be looked
at in a systems-based way; today the elements of artificial
intelligence are often embedded in physical systems and,
therefore, their features also must be respected by developers.</p>
      <p>
        One more aspect generating challenges is the different
types of relationships between the systems. This is a
wellrecognized problem which needs to be solved. In 2019 it was
deemed necessary for a standard [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], facilitating the handling
of these relationships, to be released. The same aspect also
concerns the roles of sociotechnical systems in their
environment, where frequent changes in company
relationships occur; due to their merging with other companies
or acquiring new ones and then integrating them in their
structures. These changes influence the ecosystemic balance
in the environment that must be considered in requirements
engineering so as to avoid breaking or disturbing value
networks that are essential for well-being of sociotechnical
systems, their development, and adjustment.
      </p>
      <p>The discussed features of projects and sociotechnical
systems impact knowledge content and processes in
continuous requirements engineering.
B. Knowledge Content and Processes in Continuous
Requirements Engineering</p>
      <p>
        The challenges and their treatments in continuous
requirements engineering can be considered from two
perspectives, namely, the perspective of knowledge content
and the perspective of requirements engineering processes or
activities. Regarding the knowledge content, two types of
knowledge are essential in requirements engineering – tacit
and explicit. The main factor in traditional requirements
engineering is explicit knowledge expressed in forms of
models and requirements specifications [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ]. In agile
approaches, tacit knowledge plays an essential role, as
knowledge representation and acquisitions formats are less
complex and less consistent; often leaving knowledge
integration results undocumented [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]. Both perspectives will
be considered in the two following sections that focus on some
of the continuous requirements engineering challenges and
treatments.
      </p>
      <p>III. CHALLENGES AND TREATMENTS IN AGILE PROJECTS</p>
      <p>
        Requirements engineering challenges in agile projects
have been under the watch of researchers for several years [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ].
Recently, two surveys were published about this topic [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
These surveys are used in this section to discuss the challenges
and treatments from the perspectives of knowledge content,
its distribution [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ], and requirements engineering activities.
The discussion follows the structuring of challenges in (partly
overlapping) groups proposed in [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], also adding to each
group some of the issues discussed in [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
      </p>
      <p>
        Group1: Build and maintain shared understanding of
customer value [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], direct communication with stakeholders
[
        <xref ref-type="bibr" rid="ref4">4</xref>
        ], less preliminary planning and focus, no initial team
involvement [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ], tacit knowledge [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. As agile approaches rely
upon tacit knowledge, it is challenging to understand customer
value without direct communication. On the other hand, direct
communication is time-consuming and the benefit from it is
perceived mainly by those involved in the communication. So,
the essential questions here are: when who should
communicate with whom and how acquired knowledge can
and should be further distributed.
      </p>
      <p>
        Group 2: Support change and evolution [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], changing
requirements [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. While well-defined requirements
management procedures are available in conventional
requirements management tools, handling changes in vaguely
defined requirements procedures is a new problem. Here, the
main questions are how to identify the change, how to see its
impact on other requirements, and how to know when, to
whom, and how the changes should be communicated.
      </p>
      <p>
        Group 3: Build and maintain shared understanding about
system [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], lack of documentation [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. To meet this challenge,
systems thinking, and the appropriate amount of
documentation are seen as possible treatments. When
considering the number of views, possible levels of
decomposition and abstraction, and information/knowledge
dependencies and their flows between developers and
stakeholders, continuous maintaining of a valid shared body
of knowledge seems to be a task of a very high complexity.
      </p>
      <p>
        Group 4: Representation of requirements knowledge [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]:
manage levels of decomposition, consistency, quality of
requirements, etc; missing, ambiguous, and conflicting
requirements [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ], negligence of non-functional requirements,
inability of customer in telling user stories [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. Whereas
•
•
•
•
•
•
Group 3 concerned overall knowledge about the
sociotechnical system, this group of challenges directly
concerns the knowledge about requirements. More
specifically, requirements knowledge may be missing, may be
represented inappropriately or not at the right level of
decomposition. It seems that the problems with requirements
knowledge do not differ from those of Group 3, therefore the
same tools might be used for handling both of these groups of
challenges.
      </p>
      <p>
        Group 5: Process aspects [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], such as prioritization,
managing completeness, consistency, and quality of
requirements; also, requirements prioritization in [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. Some
approaches, such as staged frameworks [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ], clear hierarchy of
teams, backlog combinations [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], and taxonomies are
proposed for handling these problems, while acknowledging
that there are no agreed upon means for managing complexity
of requirements.
      </p>
      <p>
        Group 6: Organizational aspects [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] such as bridging plan
driven and agile, planning validation and verification based
on requirements, allocating time for invention and planning,
and seeing the impact on infrastructure. System-level
awareness, iterations in planning and innovation, actively
managed boundary objects are some of the suggested
treatments [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ].
      </p>
      <p>Common treatments that are suggested in several groups
of challenges are the following:</p>
    </sec>
    <sec id="sec-2">
      <title>Holistic view requirements on sociotechnical systems and</title>
    </sec>
    <sec id="sec-3">
      <title>Respecting and introducing hierarchies Establishing and maintaining the traceability between knowledge items</title>
    </sec>
    <sec id="sec-4">
      <title>Well-organized communication</title>
      <p>These aspects suggest that a well-defined and, at the same
time, flexible system or structure of knowledge is expected to
lie behind the methods and tools of continuous requirements
engineering in agile settings. Systems aspects, from a different
perspective, are discussed further in the next section.
IV. ENTERPRISES AND ECOSYSTEMS: A SYSTEMS-BASED VIEW</p>
      <p>
        When looking from an enterprise and ecosystem
perspective on continuous requirements engineering, two
issues become the main sources of challenge: (1) the diversity
of system types (social, software, hardware, physical,
biological, etc.) and (2) diversity of relationships between the
systems. The challenges stemming from the diversity of the
systems will be discussed in the context of
socio-cyberphysical systems [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. The challenges regarding the diversity
of relationships between systems will be discussed based on
research in the Systems of Systems area [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ], [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ], [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ].
A. Diversity of Systems in Sociotechnical Contexts
      </p>
      <p>
        In requirements engineering, the diversity of systems
requires consideration of a large amount of data, information,
and knowledge flows, that are, for instance, produced by
systems of different natures [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]:
      </p>
    </sec>
    <sec id="sec-5">
      <title>Mechanical hardware components Computing hardware components that can be standalone (computers) or those embedded in mechanical hardware (smart devices)</title>
      <p>•
•
•
•
•</p>
      <p>Software components that are installed on computing
hardware
Human components that can form different social
structure components</p>
      <p>
        Data and knowledge can be part of computing software,
human or social components. Data (as a components) are used
for communication; and data, information, and knowledge are
exchanged between all other components. Data can be
processed, transformed into information, and saved as
knowledge in different ways. Thus, the diversity of systems
causes a hard to manage diversity of data, information, and
knowledge that needs to be handled in continuous
requirements engineering. Besides these problems (and partly
because of them), cyber-physical contexts yield similar
problems to those discussed with respect to agile
environments (levels of decomposition of knowledge,
different lengths of activities, lack of tools for knowledge
handling, etc.) [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ].
      </p>
      <p>Additionally, such issues as openness of systems, the
necessity to consider their real time behavior in several
contexts, and their natural and artificial intelligence-based
adaptability, contribute to the complexity of analyzing,
representing, and planning for requirements engineering in
sociotechnical systems.</p>
      <p>B. Diversity of Relationships between Systems.</p>
      <p>
        Sociotechnical systems form various types of systems of
systems; for instance, directed, acknowledged, collaborative,
and virtual systems [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. The patterns of relationships are
different in each of these cases and must be, first, discovered,
second, represented and respected, and then thirdly, the
changes in these relationships must be perceived and
understood so as to align the requirements with those
relationships between the systems that are actually in place at
a given point of time. Understanding of relationships between
systems is based on consideration of the following features
attributed to systems of systems [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ], [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ], [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ]:
      </p>
      <p>
        Independence, which shows that the systems which
form a larger system can operate and are managed
separately [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. It is possible to distinguish between
operational independence, managerial independence
[
        <xref ref-type="bibr" rid="ref13">13</xref>
        ], and evolutionary independence [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ].
      </p>
      <p>
        Distribution. The systems that form larger systems
can be dispersed and, also, communicate over larger
distances [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. For physical systems, such as smart
cars or traffic lights, geographical distribution is
essential [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ]. However, when considering social
systems and software, the topological distribution can
be considered with respect to social distances, code
threading, and other aspects.
      </p>
      <p>
        Emergence which is defined as the behavior of a
larger system that exceeds the behavior of the systems
that are parts of it (its constituent systems [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ]) [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. It
is possible to distinguish between three types of
emergence behaviors [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ], [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ]: simple emergence
behavior that occurs in relatively simple systems and
can be predicted; weak emergence behavior which is
the expected emergence behavior that is desired or
allowed for in the system structure, but cannot be
predicted from the knowledge of the characteristics of
the individual constituent systems; and strong
emergence behavior which is unexpected emergence
behavior that becomes evident only during system
failure and cannot be attributed to any particular
constituent system(s). This feature is the least
researched in requirements engineering and one of the
most challenging issues in continuous requirements
engineering.
      </p>
      <p>Evolution, as systems of systems are in continual
development and can never be considered fully
completed.</p>
      <p>
        One of the forms of evolution is merging of companies or
acquisition of one company by another company. These cases
are especially challenging because the identities and roles of
constituent systems change, knowledge loss is possible, and
many iterations are needed to reach consensus with respect to
the changes in social and information technology related
aspects. In these systems it is important to acquire,
accumulate, share, and process knowledge, not only about
current and future states of the system(s), but also to acquire,
accumulate, share, and process knowledge about the
implementation of changes [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ]. In the next section a possible
integration of these knowledge management activities with a
continuous requirements engineering framework will be
shown.
      </p>
      <p>V. KNOWLEDGE MANAGEMENT ENHANCED CONTINUOUS</p>
      <p>REQUIREMENTS ENGINEERING</p>
      <p>
        The challenges of continuous requirements engineering in
sociotechnical systems show that the tasks of requirements
engineering, in this context, require strong support in terms of
knowledge management both (1) in terms of the content of
knowledge to by acquired, accumulated, processed, and
shared and (2) in terms of activities and processes performed
during continuous requirements engineering. For instance,
agile and plan driven approaches are expected to be combined
[
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. One of the frameworks that allows accommodation of
different life cycles of systems development is the FREEDOM
framework [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ]. This assumes fractal organization of
knowledge regarding target systems, its context, and the
systems development processes. This framework can also
accommodate different enterprise architecture representations
regarding current and future states of sociotechnical systems
[
        <xref ref-type="bibr" rid="ref18">18</xref>
        ]; and can be supported by knowledge management
methods and tools (Fig. 2).
      </p>
      <p>
        Fractality in representing knowledge about the
sociotechnical system(s) and development processes might be
a solution for some of the challenges discussed in the previous
sections. This could allow traceability between hierarchically
well-organized pieces of knowledge that are structured
according to organizational units, processes, and development
projects [
        <xref ref-type="bibr" rid="ref19">19</xref>
        ]. It could define separate knowledge distribution
processes for development teams and help with handling
consistency between requirements at different levels of
granularity, and of different forms of representation. Thus, it
is a potential means for achieving the following suggested
treatments of the requirements engineering challenges in
sociotechnical systems that were discussed in Section III:
•
•
•
•
      </p>
      <p>Holistic view on sociotechnical systems and
requirements can be achieved as fractal knowledge
representation provides the possibility of considering
knowledge items simultaneously via “part of” and
classification relationships between knowledge
components.</p>
      <p>Respecting and introducing hierarchies is possible as
(1) hierarchies are a natural form of representation in a
fractal system, and (2) a multifractal approach (having
different hierarchies for parameters that scale the
system) can be applied so as to have both the
knowledge component hierarchies according to the
sociotechnical systems configurations and the
knowledge component hierarchies according to the
development team configurations.</p>
      <p>Establishing and maintaining the traceability between
knowledge items is possible as the fractal system
allows for preserving different types of relationships
between items belonging to different fractals.</p>
      <p>
        Well-organized communication could be achieved by
combining fractal knowledge representation with the
compliant knowledge distribution methods [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ].
      </p>
      <p>The above proposal highlights just some of the
possibilities that will further be elaborated and tested in
continuous engineering settings where sociotechnical systems
are concerned. For instance, it is not clear whether fractal
representations of knowledge can help in the handling of the
strong emergence behavior challenge, which is the least
researched challenge in continuous requirements engineering
in sociotechnical systems.</p>
      <p>VI. CONCLUSION</p>
      <p>Analysis of challenges in different requirements
engineering projects has revealed the necessity for appropriate
knowledge management methods and tools that could ensure
knowledge reuse, timely and adequate knowledge acquisition
and distribution; and establishing and representing well
recognizable relationships between knowledge components
used in systems development. This necessity emerges behind
almost all of the challenges discussed in this paper. Whilst, the
origins of the challenges are different, they are all rooted in
the lack of (1) tool-supported systems-based representation of
knowledge, as the basis for continuous requirements
engineering, and (2) a simple means to handle this knowledge
and to use it. Fractal approaches may be a solution for
knowledge representation as they allow development of
complex representations as simple combinations of
predefined and emerging components.</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          [1]
          <string-name>
            <given-names>E.-M.</given-names>
            <surname>Schön</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Thomaschewski</surname>
          </string-name>
          , and
          <string-name>
            <given-names>M. J.</given-names>
            <surname>Escalona</surname>
          </string-name>
          , “
          <article-title>Agile requirements engineering: a systematic literature review</article-title>
          ,”
          <source>Computer Standards &amp; Interfaces</source>
          , vol.
          <volume>49</volume>
          , pp.
          <fpage>79</fpage>
          -
          <lpage>91</lpage>
          ,
          <year>2017</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          [2]
          <string-name>
            <given-names>S.</given-names>
            <surname>Mosser and J.-M. Bruel</surname>
          </string-name>
          , “
          <article-title>Requirements engineering in the DevOps era</article-title>
          ,”
          <source>2021 IEEE 29th International Requirements Engineering Conference (RE)</source>
          , pp.
          <fpage>510</fpage>
          -
          <lpage>511</lpage>
          ,
          <year>2021</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          [3]
          <string-name>
            <given-names>R.</given-names>
            <surname>Kasauli</surname>
          </string-name>
          ,
          <string-name>
            <given-names>E.</given-names>
            <surname>Knauss</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Horkoff</surname>
          </string-name>
          ,
          <string-name>
            <given-names>G.</given-names>
            <surname>Liebel</surname>
          </string-name>
          ,
          <string-name>
            <given-names>F.</given-names>
            <surname>Gomes de Oliveira Neto</surname>
          </string-name>
          , “
          <article-title>Requirements engineering challenges and practices in largescale agile system development,”</article-title>
          <source>The Journal of Systems &amp; Software</source>
          , vol.
          <volume>172</volume>
          , article 110851,
          <year>2021</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          [4]
          <string-name>
            <given-names>A.</given-names>
            <surname>Rasheed</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Zafar</surname>
          </string-name>
          ,
          <string-name>
            <given-names>T.</given-names>
            <surname>Shehryar</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N. A.</given-names>
            <surname>Aslam</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Sajid</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N.</given-names>
            <surname>Ali</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S. H.</given-names>
            <surname>Dar</surname>
          </string-name>
          , and
          <string-name>
            <given-names>S.</given-names>
            <surname>Khalid</surname>
          </string-name>
          , “
          <article-title>Requirement engineering challenges in agile software development</article-title>
          ,” Mathematical Problems in Engineering, vol.
          <year>2021</year>
          , article
          <volume>6696695</volume>
          , 18 pages,
          <year>2021</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref5">
        <mixed-citation>
          <article-title>[5] Socio-technical systems, Interactive design</article-title>
          . Available: https://www.interaction-design.org/literature/topics/socio-technicalsystems
        </mixed-citation>
      </ref>
      <ref id="ref6">
        <mixed-citation>
          [6] ISO/IEC/IEEE 21839:
          <year>2019</year>
          ,
          <article-title>Systems and software engineering - System of systems (SoS) considerations in life cycle stages of a system</article-title>
          . Available: https://www.iso.org/standard/71955.html
        </mixed-citation>
      </ref>
      <ref id="ref7">
        <mixed-citation>
          [7]
          <string-name>
            <given-names>J. A.</given-names>
            <surname>Bubenko</surname>
          </string-name>
          and
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          , “
          <article-title>Improving the quality of requirements specifications by enterprise modelling</article-title>
          ,
          <source>” Perspectives on Business Modelling</source>
          , Springer, Berlin, Heidelberg, pp.
          <fpage>243</fpage>
          -
          <lpage>268</lpage>
          ,
          <year>1999</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref8">
        <mixed-citation>
          [8]
          <string-name>
            <given-names>V.</given-names>
            <surname>Gervasi</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R.</given-names>
            <surname>Gacitua</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Rouncefield</surname>
          </string-name>
          ,
          <string-name>
            <given-names>P.</given-names>
            <surname>Sawyer</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Kof</surname>
          </string-name>
          , L. Ma,
          <string-name>
            <given-names>P.</given-names>
            <surname>Piwek</surname>
          </string-name>
          , A. de Roeck,
          <string-name>
            <given-names>A.</given-names>
            <surname>Willis</surname>
          </string-name>
          ,
          <string-name>
            <given-names>H.</given-names>
            <surname>Yang</surname>
          </string-name>
          , and
          <string-name>
            <given-names>B.</given-names>
            <surname>Nuseibeh</surname>
          </string-name>
          , “
          <article-title>Unpacking tacit knowledge for requirements engineering</article-title>
          ,” Managing Requirements Knowledge, Springer, Berlin, Heidelberg, pp.
          <fpage>23</fpage>
          -
          <lpage>47</lpage>
          ,
          <year>2013</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref9">
        <mixed-citation>
          [9]
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          and
          <string-name>
            <given-names>J</given-names>
            <surname>Grundspenkis</surname>
          </string-name>
          , “
          <article-title>Using knowledge distribution in requirements engineering,” Knowledge-Based Systems</article-title>
          , pp.
          <fpage>149</fpage>
          -
          <lpage>184</lpage>
          ,
          <year>2000</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref10">
        <mixed-citation>
          [10]
          <string-name>
            <given-names>K.</given-names>
            <surname>Lace</surname>
          </string-name>
          and
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          , “
          <article-title>Required changes in requirements engineering approaches for socio-cyber-physical systems</article-title>
          ,” 24th Joint International Conference on Requirements Engineering:
          <article-title>Foundation for Software Quality Workshops, Doctoral Symposium</article-title>
          ,
          <source>REFSQ-JP 2018; Utrecht; Netherlands; 19 March</source>
          <year>2018</year>
          , CEUR Workshop Proceedings, vol.
          <year>2075</year>
          ,
          <year>2018</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref11">
        <mixed-citation>
          [11]
          <string-name>
            <given-names>C.</given-names>
            <surname>Ncube</surname>
          </string-name>
          and
          <string-name>
            <given-names>S. L.</given-names>
            <surname>Lim</surname>
          </string-name>
          , “
          <article-title>On systems of systems engineering: a requirements engineering perspective</article-title>
          and research agenda,”
          <source>2018 IEEE 26th International Requirements Engineering Conference (RE)</source>
          , pp.
          <fpage>112</fpage>
          -
          <lpage>123</lpage>
          ,
          <year>2018</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref12">
        <mixed-citation>
          [12]
          <string-name>
            <given-names>S.</given-names>
            <surname>Hallerstede</surname>
          </string-name>
          ,
          <string-name>
            <given-names>F. O.</given-names>
            <surname>Hansen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Holt</surname>
          </string-name>
          ,
          <string-name>
            <given-names>R.</given-names>
            <surname>Lauritsen</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Lorenzen</surname>
          </string-name>
          , and
          <string-name>
            <given-names>J.</given-names>
            <surname>Peleska</surname>
          </string-name>
          , “
          <article-title>Technical challenges of SoS requirements engineering</article-title>
          ,
          <source>” 2012 7th International Conference on System of Systems Engineering (SoSE)</source>
          , pp.
          <fpage>573</fpage>
          -
          <lpage>578</lpage>
          ,
          <year>2012</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref13">
        <mixed-citation>
          [13]
          <string-name>
            <given-names>F. L.</given-names>
            <surname>Duarte</surname>
          </string-name>
          ,
          <string-name>
            <surname>A</surname>
          </string-name>
          . Félix de Castro, and
          <string-name>
            <given-names>P. G. G.</given-names>
            <surname>Queiroz</surname>
          </string-name>
          , “
          <article-title>Reap-SoS: a requirement engineering approach for system of systems,” Computer Science</article-title>
          and Information Technology,
          <year>April 2018</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref14">
        <mixed-citation>
          [14]
          <string-name>
            <given-names>T.</given-names>
            <surname>Rzazade</surname>
          </string-name>
          ,
          <article-title>Continuous requirements engineering for cyberphysical systems</article-title>
          ,
          <source>Master Thesis</source>
          , Riga Technical University, Riga, Latvia,
          <year>2021</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref15">
        <mixed-citation>
          [15]
          <string-name>
            <given-names>S. E. Page. Understanding</given-names>
            <surname>Complexity</surname>
          </string-name>
          .
          <source>The Great Courses. Chantilly</source>
          ,
          <string-name>
            <surname>VA</surname>
          </string-name>
          , USA: The Teaching Company,
          <year>2009</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref16">
        <mixed-citation>
          [16]
          <string-name>
            <given-names>K.</given-names>
            <surname>Lace</surname>
          </string-name>
          and
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          , “
          <article-title>Post-merger integration specific requirements engineering model</article-title>
          ,
          <source>” Artificial Intelligence in Business Informatics, LNBIP</source>
          , vol.
          <volume>430</volume>
          , pp.
          <fpage>115</fpage>
          -
          <lpage>129</lpage>
          ,
          <year>2021</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref17">
        <mixed-citation>
          [17]
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          , “
          <article-title>Continuous requirements engineering in FREEDOM framework: a position paper</article-title>
          ,”
          <source>Joint Proceedings of REFSQ-2016 Workshops, Doctoral Symposium</source>
          , Research Method Track, and
          <article-title>Poster Track co-located with the 22nd International Conference on Requirements Engineering: Foundation for Software Quality (REFSQ</article-title>
          <year>2016</year>
          ),
          <year>March</year>
          14-17,
          <year>2016</year>
          , Gothenburg, Sweden.
          <source>CEUR Workshop Proceedings</source>
          , vol.
          <volume>1564</volume>
          ,
          <year>2016</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref18">
        <mixed-citation>
          [18]
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          , “Variable Contents of Enterprise Models,” Procedia Computer Science, vol.
          <volume>104</volume>
          , pp.
          <fpage>89</fpage>
          -
          <lpage>96</lpage>
          ,
          <year>2017</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref19">
        <mixed-citation>
          [19]
          <string-name>
            <given-names>M.</given-names>
            <surname>Kirikova</surname>
          </string-name>
          , “
          <article-title>Towards flexible information architecture for fractal information systems</article-title>
          ,” 2009 International Conference on Information, Process, and Knowledge Management, pp.
          <fpage>135</fpage>
          -
          <lpage>140</lpage>
          ,
          <year>2009</year>
          .
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>